Butler matrices, as well as the equivalent distributed feeding devices, are generally employed for microwave-frequency signals or more generally for electrical signals in the microwave-frequency range. The technology conventionally used to embody such a device is waveguide technology which exhibits the drawback of significant bulkiness. Indeed, for onboard applications, a problem to be solved relates to the miniaturization of such devices since the compactness of an antennal device is a significant advantage especially when the number of antennal elements, and therefore indirectly the number of outputs of the Butler matrix, increases.
Furthermore, for a significant number of antennal elements or of beams to be generated, typically greater than a hundred, the implementation of a Butler matrix becomes very complex since the greater the increase in the number of inputs and outputs, the greater is the impediment to hardware embodiment from the number of components and their arrangement, since the precision required notably in the phase shifts between the outputs of the matrix comes up against the limits of the technology. For this reason, when the number of inputs/outputs of a Butler matrix exceeds 8, it is necessary to use several matrices connected together within a particular arrangement, thereby further increasing the bulkiness of the complete device.
FIG. 1A represents an exemplary distributed feeding device for antenna beamforming according to the prior art. The device according to FIG. 1A is able to generate 64 different signals to feed an antennal array comprising 64 antennal elements disposed, for example, according to a matrix arrangement in a plane.
The device 100 according to FIG. 1A comprises a first assembly of eight distributed feeding circuits 101, . . . , 108 arranged in parallel in a first plane, for example a vertical plane, and a second assembly of eight distributed feeding circuits 111, . . . 118 arranged in parallel in a second plane, orthogonal to the first plane, for example a horizontal plane. Each output of a circuit 101, . . . 108 of the first assembly is connected to an input of a different circuit 111, . . . 118 from the second assembly.
The overall arrangement of the 16 identical feeding circuits makes it possible to obtain a device with 64 inputs I1, . . . , I8, . . . I57, . . . I64 and 64 outputs O1, . . . , O8, . . . O57, . . . O64. The circuits used are for example Butler matrices. The arrangement thus produced makes it possible to obtain a device equivalent to a Butler matrix with 64 inputs and 64 outputs with controllable phase shifts. When one of the inputs of the device is activated, the signals obtained on the outputs of one and the same feeding circuit 111, . . . 118, exhibit phase shifts with a constant increment between two adjacent outputs and the signals obtained on a vertical row consisting of an output of each of the feeding circuits 111, . . . 118, of the second assembly also exhibit phase shifts with a constant increment between two adjacent outputs of the row.
FIG. 1B represents a distributed feeding device 110 of the same type as that of FIG. 1A in which the feeding circuits used are Rotman lenses. These circuits exhibit the particular feature of not being limited to equal numbers of inputs and of outputs.
The device 110 of FIG. 1B comprises a first assembly 111 of six circuits LR1 of the Rotman lens type each comprising 8 inputs I1, . . . I8 and I6 outputs.
The device 110 furthermore comprises a second assembly 112 of 16 circuits LR2 of the Rotman lens type each comprising six inputs and twelve outputs.
The first and the second assembly are arranged so that the outputs of the circuits of the first assembly are connected to the inputs of the circuits of the second assembly.
In this manner, the device 110 makes it possible to feed an antennal array comprising 12*16=192 radiating elements.
A drawback of the devices according to FIGS. 1 and 1b is their bulkiness and the number of components required for their embodiment. Indeed, they require a significant number of basic circuits (16 for the case of FIG. 1A, 22 for the case of FIG. 2) each consisting of a plurality of hybrid couplers and of phase shifters.
A problem to be solved consists in decreasing the bulkiness and the number of components required to embody a distributed feeding device for beamforming comprising a number greater than 8, for example equal to 64, of inputs and of outputs.
The invention proposes a distributed feeding device for antenna beamforming whose bulkiness is substantially decreased with respect to the prior art solution described in FIG. 1A.
In its best embodiment, the invention requires only the use of two distributed feeding circuits which are connected so as to generate 64 beams instead of 16 circuits as in the example of FIG. 1A.